I'm running an SBS2011 Server and a few months ago I updated Exchange from SP2 to SP3. Ever since the update we have had some strange issues like email disappearing from Outlook but still showing up on our phones or OWA. Having to click send/receive on Outlook sometimes to get new emails in. New emails not showing up until we close Outlook and reopen, task flags not updating until we close Outlook and reopen. This happens on different computers, different users and different versions of Outlook (2013 & 2016). Some emails will disappear from Outlook once they have been opened but still show up on our phones or OWA. I am stumped!